Janggu is the most widely used instrument for jangdan (rhythmic pattern) among the Korean drum family. It is used in practically every form of Korean music. It consists of an hourglass-shaped body with two heads made from animal skins. The two heads produce sounds of different pitch and timbre, which are believed to represent yin and yang. Different sizes are used for different types of music: A-ak (a large sized version of the Janguu) is used in folk music, while Jeong-ak (a small sized version of the Janggu) is used with dancers, who carry it suspended from one shoulder, held diagonally to their torso. The design of the eJanggu involved many experiments with how the modification would effect the sound the instrument. One major test involved using a laser cutter to construct a custom plug inside the instrument to separate the sound of the left and right cavities to eliminate cross talk from the two microphone installed on either side. It was found, as expected, that this greatly effected the bass response of the instrument. However it did greatly improve the isolation of each microphones as clean signals in the mid-frequency range. Sensors were embedded into the eJanggu in a similar fashion to the eHaegum. Knobs and buttons were embedded directly into the shell of the instrument. Because the Janggu has a much larger cavity, the Arduino MEGA was chosen as the microcontroller with options for many more analog-to-digital converters and digital pins for design. The accelerometer was embedded, so that when the eJanggu was used with a dancing performer, they would get control of 3-axis of acceleration data. Two infrared sensors were installed. This configuration was chosen to capture data about how the Janggu is performed traditionally. There is a technique where the left hand crosses the drum and performs both sticks on the right hand skin. The infrared sensors were installed to sense what direction the hand is moving (left to right , right to left) so that the software can have intelligence on weather both hands are on the right hand skin or if each hand is on either side of the drum.
The Korean Digital Folk Drum